1. Field of the Invention
The present invention relates to a dielectric duplexer and a communication device including such dielectric duplexer.
2. Description of the Related Art
A conventional dielectric duplexer to be used for mobile communication devices such as mobile phones, portable telephones, etc. is shown in FIGS. 10 and 11. The dielectric duplexer 21 has five resonator holes 2a, 2b, 2c, 2d and 2e formed, which pass through a pair of end surfaces 1a, 1b facing each other of a dielectric block 1 which is substantially rectangular, parallelepiped-shaped. Each of the resonator holes 2a through 2e has a large-in-diameter hole portion 15 circular in cross-section and a small-in-diameter hole portion 16 circular in cross-section linked to the large-in-diameter hole portion 15. (In FIG. 10, the construction of the resonator holes 2a, 2d, 2e in the dielectric block 1 is not illustrated.)
On nearly the whole external surface of the dielectric block 1, an outer conductor 4 is formed. A transmission side electrode Tx, a reception side electrode, and an antenna side electrode ANT are formed on the external surface of the dielectric block 1, spaced a fixed distance away from the outer conductor 4 in order to be non-conductive to the outer conductor 4.
On nearly the whole internal surface of each of the resonator holes 2a through 2e an inner conductor 3 is formed, with a gap 18 between the inner conductor 3 and a portion of the outer conductor 4 which extends into the opening portion of the large-in-diameter hole portion 15 a gap 18 is given. The end surface 1a on the side of the large-in-diameter hole portions 15 is referred to as an open-circuit end surface, and the end surface 1b on the side of the small-in-diameter hole portions 16 is referred to as a short-circuit end surface. The inner conductor 3 is electrically separated from the outer conductor 4 at the open-circuit end surface 1a, and is electrically short circuit connected to the outer conductor 4 at the short-circuit surface 1b. Further, the length in the axial direction of each of the resonator holes 2a through 2e is .lambda./4. (The Symbol .lambda. represents the central wavelength of the resonator formed by each of the resonator holes 2a through 2e.)
The above dielectric duplexer 21 is composed of a transmission side filter 10A made up of the two resonators formed from the resonator holes 2a, 2b and a reception side filter 10B made up of the three resonators formed from the resonator holes 2c, 2d and 2e. And between these filters 10A, 10B and the transmission side electrode Tx, reception side electrode Rx, and antenna side electrode ANT, an electromagnetic coupling is required. Because of this, on the left-hand side of the resonator hole 2a a transmission side excitation hole 5a and a transmission side external coupling adjustment hole 6a are formed. Between the resonator holes 2b and 2c an antenna side excitation hole 5b and an antenna side external coupling adjustment hole 6b are formed, and on the right-hand side of the resonator hole 2e a reception side excitation hole 5c and a reception side external coupling adjustment hole 6c are formed. (In FIG. 10, the construction of the excitation holes 5a through 5c and the external coupling adjustment holes 6a through 6c inside the dielectric block 1 is not illustrated.)
On the whole internal surface of the excitation holes 5a through 5c and the external coupling adjustment holes 6a through 6c an inner conductor 3 is formed respectively. The excitation holes 5a, 5b and 5c pass through the transmission side electrode Tx, antenna side electrode ANT, and reception side electrode Rx respectively. That is, the inner conductor 3 of each of the excitation holes 5a through 5c is electrically connected to the outer conductor 4 at the open-circuit end surface 1a, and is electrically separated from the outer conductor 4 at the short-circuit end surface 1b. On the other hand, the external coupling adjustment holes 6a, 6b and 6c are formed parallel with the excitation holes 5a through 5c in the vicinity of each of the excitation holes 5a to 5c, and the inner conductor 3 of each of the external coupling adjustment holes 6a to 6c is electrically connected to both the open-circuit end surface 1a and the short-circuit end surface 1b.
By changing the location, shape and inner dimension (size) of the external coupling adjustment holes 6a through 6c, the self-capacitance of the excitation holes 5a through 5c can be increased or decreased, and accordingly the degree of external coupling can be changed to establish a more appropriate external coupling. The self-capacitance of the excitation holes 5a through 5c means a capacitance generated between the inner conductor 3 of the excitation holes 5a through 5c and the ground conductor (including the outer conductor 4 and the inner conductor 3 of the external coupling adjustment holes 6a through 6c).
In this construction, the transmission side excitation hole 5a and the transmission side external coupling adjustment hole 6a are electromagnetically coupled with the resonator hole 2a neighboring those holes 5a, 6a. The antenna side excitation hole 5b and the antenna side external coupling adjustment hole 6b are electromagnetically coupled with the resonator holes 2b, 2c neighboring the holes 5b, 6b. The reception side excitation hole 5c and the reception side external coupling adjustment hole 6c are electromagnetically coupled with the resonator hole 2e neighboring the holes 5c, 6c. The external coupling is realized through these electromagnetic couplings. The dielectric duplexer 21 thus constructed outputs a transmission signal which enters the transmission side electrode Tx from a transmission circuit system not illustrated, and exits from the antenna side electrode after passing through the transmission side filter 10A. The dielectric duplexer 21 outputs a reception signal which enters from the antenna side electrode ANT, passes through the reception side filter 10B and exits to a reception circuit system not illustrated, from the reception side electrode Rx.
In this way, in the conventional dielectric duplexer 21, the excitation holes 5a, 5b, 5c were required in order to realize the electromagnetic coupling between the filters 10A, 10B and the transmission side electrode Tx, reception side electrode Rx, and antenna side electrode ANT. Further, because an especially high electromagnetic coupling is required between the antenna side electrode ANT and the filters 10A, 10B, it is difficult to shorten the spacing between the antenna side excitation hole 5b and the resonator holes 2b, 2c by adjusting the position of the antenna side external coupling adjustment hole 6b. In this dielectric duplexer, relatively long spacing is needed between the antenna side excitation hole 5b and the resonator holes 2b, 2c. Because of this, it is difficult to reduce the width of the conventional dielectric duplexer 21.